JP4502329B2 - Compression self-ignition internal combustion engine - Google Patents

Description

  The present invention relates to a compression self-ignition internal combustion engine.

  In recent years, in the field of internal combustion engines such as diesel engines, stricter exhaust regulations have been enforced year by year due to the growing environmental problems, reducing emissions of soot, smoke, CO, NOx and other air pollutants, and fuel consumption There is a strong demand for improvement.

  However, since diesel engines spray fuel on compressed air in a cylinder and burn it by self-ignition, light and dark mixing tends to occur in the mixture of air and fuel, and soot and smoke can be produced where the fuel concentration is high. It is easy to generate NOx near the theoretical ratio.

  In view of such circumstances, Patent Document 1 below attempts to suppress the generation of NOx and reduce the discharge of graphite and HC. Specifically, a concave head cavity is formed on the explosion surface of the cylinder head facing the top surface of the piston, a fuel injection nozzle is provided at the bottom of the head cavity, and a concave piston cavity is provided on the top surface of the piston. It has become a thing. The head cavity is formed in a dome shape or a cone shape, and the fuel injection nozzle is configured to inject fuel toward the peripheral wall surface of the head cavity.

JP 10-141622 A

  In the configuration in which the fuel injected from the fuel injection nozzle collides with the peripheral wall surface of the head cavity as in Patent Document 1, adhesion of fuel to the peripheral wall surface becomes a problem. In particular, the temperature in the combustion chamber is low when the engine is started or during low-load operation, so that the fuel that has contacted the peripheral wall is less likely to evaporate. Is more likely.

  An object of the present invention is to suppress the generation of white smoke due to the adhesion of fuel to a peripheral wall surface in a compression self-ignition internal combustion engine of a type in which fuel collides with the peripheral wall surface of a head cavity formed in a cylinder head. And

According to a first aspect of the present invention, there is provided a fuel injection nozzle in which a concave head cavity is provided on the explosion surface of the cylinder head facing the top surface of the piston, and fuel is injected into the head cavity toward the peripheral wall surface of the head cavity. In a compression self-ignition internal combustion engine provided with a temperature detecting means for detecting the temperature of the peripheral wall surface of the head cavity, and a controller for setting the fuel injection timing and the number of injection stages based on the detected peripheral wall surface temperature And the controller predicts the amount of fuel adhering to the peripheral wall surface of the head cavity and the evaporation amount of fuel contacting the peripheral wall surface based on the peripheral wall surface temperature detected by the temperature detecting means. Further, the present invention is characterized in that it has a function of setting the fuel injection timing and the number of injection stages based on a comparison between the predicted adhesion amount and evaporation amount .

According to a second aspect of the present invention, in the first aspect of the invention, when the controller divides the number of injection stages into two stages, the first stage injection quantity is set within a range of 30% to 50% of the total injection quantity. It has the function to perform.

According to a third aspect of the invention, in the first aspect of the invention, when the controller divides the number of injection stages into two stages, the self-ignition accompanying the first stage injection is performed near the top dead center of the compression stroke. In addition, the first stage injection start timing is set within a range of 40 ° to 0 ° before the top dead center of the compression stroke.

According to a fourth aspect of the present invention, in the first aspect of the invention, there is provided an effective compression ratio changing means for changing an effective compression ratio in the cylinder, and when the adhesion amount is a predetermined amount or more with respect to the evaporation amount. The effective compression ratio changing means is controlled so as to increase the effective compression ratio and decrease the effective compression ratio when the effective compression ratio is less than a predetermined value.

According to a fifth aspect of the present invention, in the first aspect of the invention, a heater for heating the peripheral wall surface of the head cavity is provided.

According to a sixth aspect of the invention, in the fifth aspect of the invention, the temperature rises when the detected peripheral wall temperature is lower than a predetermined target value, and the temperature drops when the detected peripheral wall temperature is higher (for example, power consumption). The heater is controlled so that the heater is turned off in order to suppress this).

According to a seventh aspect of the invention, in the sixth aspect of the invention, the heater is provided partially corresponding to a portion of the head cavity peripheral wall where the fuel collides.

According to the first aspect of the present invention, for example, when the temperature of the peripheral wall surface of the head cavity is low, it is considered that the amount of fuel attached increases, so that the number of injection stages is increased. As a result, the amount of injection at each stage is reduced, so that the adhesion of fuel to the peripheral wall surface of the head cavity can be reduced, and as a result, the generation of white smoke can be suppressed. Furthermore, more accurate and fine fuel injection control can be performed in consideration of the amount of fuel adhering to the peripheral surface of the head cavity and the amount of evaporation.

According to the second aspect of the present invention, the injection amount of each stage is appropriately set, and it is possible to more reliably prevent the fuel from adhering to the peripheral wall surface of the head cavity, and to reliably reduce the heat loss caused by the fuel injection. Can be self-ignited.

According to the third aspect of the present invention, even if the first-stage injected fuel adheres to the peripheral wall surface of the head cavity, it is possible to ensure a sufficient time to evaporate by being exposed to the surrounding gas. It is possible to reliably burn near the top dead center of the compression stroke. Furthermore, by performing the second-stage injected fuel near the top dead center of the compression stroke, reliable temperature rise and combustion can be realized. Accordingly, it is possible to suitably burn substantially the entire amount of injected fuel.

According to the fourth aspect of the present invention, when the amount of fuel adhering to the peripheral wall surface of the head cavity is predicted to be greater than or equal to a predetermined amount with respect to the evaporation amount, the cylinder internal temperature is increased by increasing the effective compression ratio. Evaporation can be promoted.

According to the fifth aspect of the present invention, it is possible to promote the evaporation of the fuel in contact with the peripheral wall surface of the head cavity and to suppress the generation of white smoke.

According to the invention of claim 6 , when the peripheral wall surface temperature of the head cavity is lower than the target value, a desired evaporation characteristic can be obtained by raising the temperature by the heater, and when the temperature is higher than the target value, Energy consumption can be reduced by reducing the temperature rise caused by the heater. Therefore, it is possible to efficiently evaporate the fuel in contact with the peripheral wall surface of the head cavity without using wasted energy.

According to the invention of claim 7 , it is possible to intensively warm the space in which the fuel exists, to obtain efficient evaporation characteristics, and to reduce energy consumption.

  FIG. 1 is a schematic view of a diesel engine that is a compression premixed internal combustion engine according to an embodiment of the present invention. In this diesel engine, a piston 11 is slidably fitted to a cylinder 10, and an intake hole 14, an exhaust hole 15, and a fuel injection nozzle 13 are provided in a cylinder head 12. In the intake hole 14 and the exhaust hole 15, an intake valve 17A and an exhaust valve 17B driven by valve gears 70 and 71, respectively, are arranged.

  An engine controller 66 and a supercharger 67 are provided as engine peripheral devices. The intake hole 14 communicates with the outside air through the intake passage 73, the compressor portion 75 of the supercharger 67, and the intake pipe 76, and the exhaust hole 15 communicates with the exhaust passage 77, the turbine portion 78 of the supercharger, and the exhaust pipe 79. It communicates with the outside air through.

  The engine controller 66 includes an injection nozzle ECU 83 and a valve gear ECU 84 as well as an arithmetic unit and various storage devices. The fuel injection nozzle 13 and the valve operating devices 70 and 71 are connected to the output portion of the engine controller 66. The fuel injection nozzle 13 is controlled by the injection nozzle ECU 83 for the fuel injection amount, the fuel injection start timing, and the like. In the devices 70 and 71, the valve opening / closing timing is controlled by the valve operating device ECU84. A cooling water temperature sensor 88, a combustion pressure detection sensor 89, an intake air temperature sensor 86, and a wall temperature detection sensor 90 are connected to the input portion of the engine controller 66.

  The valve operating device 71 of the exhaust valve 15 is a variable valve operating device that can change the valve closing timing and can temporarily reopen the exhaust valve 15 during the compression stroke. The variable valve operating device 71 for the exhaust valve is a constituent element of an effective compression ratio changing unit that changes the effective compression ratio of the combustion chamber 18 as will be described later.

[Description of basic components]
Hereinafter, each structure of the piston 11, the cylinder 10, and the fuel injection nozzle 13, which are basic components of the engine, and their mutual relationship will be described in detail.

[Configuration of Piston 11]
FIG. 2 is a cross-sectional view of a cylinder top portion of a diesel engine to which the present invention is applied, and particularly shows a state where the piston 11 is in the vicinity of the top dead center. A concave piston cavity 20 is formed on the top surface of the piston 11. A central protrusion 21 that protrudes toward the cylinder head 12 is formed at the center of the bottom of the piston cavity 20, and the central protrusion 21 has a large outer diameter at the base (bottom) and a smaller outer diameter at the top. The outer peripheral surface 22 is an inclined surface that is inclined so as to expand toward the anti-cylinder head 12 side. C is attached to the expansion angle of the outer peripheral surface 22.

  The bottom surface 24 of the piston cavity 20 is formed in an arc surface that is gently connected to the inclined surface 22 of the central projecting portion 21. The outer peripheral surface 25 of the piston cavity 20 is formed as a circular arc surface continuous from the bottom surface 24 and extends to the top surface of the piston 11. The opening 26 of the piston cavity 20 is slightly inward in the radial direction from the outer peripheral surface 25, thereby forming a lip portion 27 that protrudes inward in the radial direction. In FIG. 2, φY is given to the opening diameter of the piston cavity 20, and φZ is given to the maximum outer diameter of the outer peripheral surface 25 of the piston cavity 20.

[Configuration of Cylinder Head 12]
FIG. 3 is an enlarged sectional view showing the head cavity and the fuel injection nozzle. As shown in FIGS. 2 and 3, a concave head cavity 29 is provided on the explosion surface 28 of the cylinder head 12 facing the top surface of the piston 11, and the head cavity 29 is formed in a truncated cone shape. Has been. That is, the bottom surface 30 of the head cavity 29 is formed as a flat surface substantially parallel to the explosion surface 28, and the peripheral wall surface 31 of the head cavity 29 is inclined in an expanding manner toward the piston 11 side (lower side). ing. In FIG. 2, φX is attached to the opening diameter of the head cavity 29, and A is attached to the opening angle of the peripheral wall surface 31 in FIG. 3.

  4 is a cross-sectional view taken along the line IV-IV in FIG. The cylinder head 12 is provided with two intake and exhaust valve seats 33, and each valve seat 33 is provided with intake and exhaust valves 17A and 17B. The head cavity 29 is surrounded by the four valves 17 </ b> A and 17 </ b> B and is sized to circumscribe each valve seat 33. However, even if it does not necessarily circumscribe each valve seat 33, it can be formed as large as possible within the range of the circumscribed circle.

  As shown in FIG. 3, in this embodiment, a fuel collision portion 34 formed of a material different from the cylinder head 12 is provided on the peripheral wall surface 31 of the head cavity 29. The fuel collision portion 34 has a width over the entire depth of the head cavity 29 and is formed to have a uniform thickness over the width. As a raw material, what has heat resistance and heat insulation is used, for example, SUS heat-resistant steel etc. are used. However, the fuel collision part 34 may be omitted, and the peripheral wall surface 31 may be made of the material of the cylinder head 12 itself.

[Configuration of Fuel Injection Nozzle 13]
As shown in FIG. 2, a fuel injection nozzle 13 is provided at the center of the bottom surface 30 of the head cavity 29. The injection nozzle 13 has a small-diameter portion 36 that accommodates a needle valve in the lower portion, and a large-diameter portion 37 that is larger in diameter than the small-diameter portion 36 in the upper portion. A stepped portion 38 is formed in the upper portion. The injection nozzle 13 is attached to a holding hole 39 formed in the cylinder head 12 via a holder 40. The holder 40 is formed in a cylindrical shape, and the inside of the cylinder is formed in a shape that matches the outer shape of the injection nozzle 13. Between the inner surface of the holder 40 and the small-diameter portion 36, a cylindrical first sealing material 41 is provided to keep the airtight therebetween, and an annular second seal is provided between the holder 40 and the step portion 38. A material 42 is interposed. The tip of the holder 40 is exposed on the bottom surface of the head cavity 29 through the holding hole 39. In addition, a bent portion 43 protrudes from the front end portion of the holder 40 in the radially inward direction, and the first seal material 41 is received from the lower side by the bent portion 43.

  As shown in FIG. 3, a plurality of fuel injection ports 44 are formed at the tip of the injection nozzle 13. Four to ten fuel injection ports 44 are formed radially about the nozzle axis O1. Each injection port 44 opens toward the peripheral wall surface 31 (fuel collision part 34) of the head cavity 29, respectively.

[Relationship Between Head Cavity 29 and Fuel Injection Nozzle 13]
As shown in FIG. 2, the fuel injected from the fuel injection port 44 of the injection nozzle 13 diffuses in a radial direction conically or horizontally as a whole. If the diffusion angle (spray angle) of the spray axis X1 at this time is B (see FIG. 3), 120 ° ≦ B ≦ 180 ° is set. By setting in this way, the fuel directly collides with the peripheral wall surface 31. By this collision, the fuel is changed in direction and atomized, and mixing with air is further promoted.

  If the spray angle B is set to 120 ° or more, it is necessary to form the head cavity 29 deep in order to cause the fuel to collide with the peripheral wall surface 31 of the head cavity 29. This is because it involves a change in structure. The reason why the spray angle B is set to 180 ° or less is that if it is more than that, the flow coefficient in the injection nozzle 13 decreases. Further, a large amount of fuel diffuses to the upper side (the bottom surface 30 side) in the head cavity 29, and the fuel concentration in the portion becomes high, which causes the generation of smoke.

  On the other hand, the expansion angle A (see FIG. 3) of the peripheral wall surface 31 of the head cavity 29 is set to 60 ° ≦ A ≦ 120 °. When the expansion angle A is set to 60 ° or more, if it is less than that, the mixing of the fuel after colliding with the peripheral wall surface 31 and a large amount of air existing radially outside in the cylinder 10 is promoted. This is because it becomes difficult to prevent formation of a uniform air-fuel mixture. In addition, the fuel that has collided with the peripheral wall surface 31 of the head cavity 29 is diffused to the upper side in the head cavity 29, and smoke is likely to be generated due to excessive fuel concentration in the head cavity 29. The reason why the expansion angle A is set to 120 ° or less is to ensure that the fuel that has collided with the peripheral wall surface 31 is introduced into the piston cavity 20.

  The intersection angle D on the piston 11 side between the peripheral wall surface 31 of the head cavity 29 and the fuel spray axis X1 is set to 120 ° ≦ D <180 °. If this D is 120 ° or less, the diffusion of fuel to the upper side in the head cavity 29 increases and smoke is likely to be generated, and if it is 180 ° or more, the fuel substantially reaches the peripheral wall surface 31 substantially. This is because they will not collide.

  The head cavity 29 has a bottom surface 30 formed on a flat surface substantially parallel to the explosion surface 28 of the cylinder head 12, and a corner 47 is formed at the boundary between the bottom surface 30 and the peripheral wall surface 31, as shown in FIG. Has been. Due to the presence of the corner portion 47, a space R wider than the conventional technique (dome-shaped or conical head cavity) is secured on the upper side in the head cavity 29. Therefore, even if the fuel that collided with the peripheral wall surface 31 of the head cavity 29 diffuses to the upper side (the bottom surface 30 side) of the head cavity 29, mixing with air is promoted as compared with the prior art.

  The fuel is in the form of a liquid column immediately after exiting from the fuel injection port 44 and then reaches the peripheral wall surface 31 while diffusing in a mist form. In the present embodiment, the distance (length) L of the spray axis X1 from the fuel injection port 44 to the peripheral wall surface 31 and the diameter φd of the fuel injection port 44 are set in a relationship of L / φd ≧ 50. By setting in this way, the liquid column portion S1 (the length is indicated by L1) of the fuel S hardly collides and adheres directly to the peripheral wall surface 31.

  If the liquid columnar fuel adheres to the peripheral wall surface 31 of the head cavity 29 during low load operation such as when starting the engine, white smoke is discharged without being involved in combustion. Such a problem can be solved by setting the diameter φd. The above relationship between the distance L and the diameter φd is particularly effective when the fuel injection pressure is about 50 MPa or more.

  As described above, the fuel collision portion 34 having heat insulation and heat resistance is provided on the peripheral wall 31 of the head cavity 29. Although the cylinder head 12 is cooled by the cooling water, the temperature of the fuel collision part 34 is difficult to be lowered due to the heat insulating property when the engine is warm. Therefore, the fuel that has collided with the fuel collision part 34 is easily evaporated by the heat of the fuel collision part 34, and the attached fuel is prevented from being discharged as white smoke.

  As shown in FIG. 4, the head cavity is provided so as to circumscribe the four valve seats 33 for intake and exhaust. That is, the valve seat 33 is formed to the maximum extent that does not erode. As a result, the distance from the fuel injection nozzle 13 to the peripheral wall surface 31 of the head cavity 29 can be made as long as possible, and the liquid column portion S1 of the fuel is prevented from adhering to the peripheral wall surface 31.

[Relationship between head cavity and piston cavity]
As shown in FIG. 2, the opening diameter φX of the head cavity 29 is formed smaller than the diameter φY of the opening 26 of the piston cavity 20. Specifically, there is a relationship of φY ≧ 1.2 × φX. Therefore, most of the fuel injected from the injection nozzle 13 and colliding with the peripheral wall surface 31 of the head cavity 29 is introduced into the piston cavity 20. The squish flow into the piston cavity 20 during the compression stroke and the reverse squish flow outside the piston cavity 20 during the expansion stroke cause a strong turbulence in the flow of the fuel, and the air flows outside the piston 11 in the radial direction. Mixing is promoted more.

  The diameter φY of the opening 26 of the piston cavity 20 is formed smaller than the outer diameter (maximum outer shape) φZ of the outer peripheral surface 25 of the piston cavity 20, and the opening 26 has a lip portion protruding radially inward. Since 27 is formed, a stronger squish flow and a reverse squish flow can be obtained.

[Relationship between injected fuel and piston cavity 20]
As shown in FIG. 2, the protrusion 21 formed in the piston cavity 20 is formed in a mountain shape as described above, and the expansion angle C of the outer peripheral surface 22 is set to C ≦ 140 °. Yes. The fuel injected from the injection nozzle 13 and colliding with the head cavity 29 collides with the inclination of the outer peripheral surface 22 of the projecting portion 21 in the piston cavity 20 while spreading further in a conical shape. Therefore, even after colliding with the projecting portion slope 22, the fuel is further guided radially outward to promote mixing with air.

  The diameter φV of the portion where the fuel collides with the piston cavity 20 and the maximum outer diameter φZ of the piston cavity 20 have a relationship of φV ≧ 0.5 × φZ. Therefore, the fuel spreads radially outward in the piston cavity and promotes mixing with air. As a result, the fuel is injected near the center of the piston cavity 20 to prevent the occurrence of “thermal pinch” in which the flame contracts without using air radially outward.

  The fuel injection may be performed not only when the piston 11 is substantially at the top dead center, but also in the range of 40 ° to 0 ° before the top dead center as will be described later. Further, there is a case where the delay is made in the range of 0 ° to 40 ° after the top dead center is passed mainly for NOx reduction. In such a case, if the injected fuel is injected out of the piston cavity 20, the generation of a uniform air-fuel mixture is hindered and smoke is increased. Therefore, in the present embodiment, when the piston 11 is within the range of the crank angle ± 40 ° from the top dead center, the fuel injection angle B and the peripheral wall surface are ensured so that the injected fuel surely enters the piston cavity 20. An expansion angle A of 31, an opening diameter φY of the piston cavity 20 and the like are set.

  In the present embodiment, when the fuel spray axis X1 that collides with the peripheral wall surface 31 spreads out to the maximum in the radial direction, that is, after the fuel spray axis X1 collides with the peripheral wall surface 31, The spray axis X1 is set so as to enter the piston cavity 20 in the range of top dead center ± 40 °, assuming a case where diffusion occurs along the inclination of the wall surface 31.

[Control of fuel injection nozzle by engine controller]
Next, control of the fuel injection nozzle 13 by the engine controller 66 will be described.
FIG. 5 is a time chart showing a fuel injection pattern by the fuel injection nozzle 13. The fuel injection nozzle 13 of this embodiment is controlled to operate in two fuel injection modes by the injection nozzle ECU 83 of the engine controller 66 (FIG. 1). One is a normal mode in which fuel injection is started almost at the top dead center (after about 10 ° before the top dead center) in the compression stroke, as shown in FIG. 5 (A), and the other is FIG. ) Is an active mode in which a part of the total fuel injection amount is injected before the compression stroke top dead center (40 ° to 0 ° before top dead center).

  When fuel is injected in the normal mode when the temperature in the cylinder is low, such as when the engine is started or during low load operation, fuel adheres to the peripheral wall surface 31 of the head cavity 29, causing white smoke. Therefore, in such a case, by switching to the active mode, the injection amount of each stage is reduced, the fuel adhesion to the peripheral wall surface 31 is reduced, and almost all of the injected fuel can be burned. .

[Control method 1]
As a method for switching between the normal mode and the active mode, in the present embodiment, the amount of injected fuel adhering to the peripheral surface 31 of the head cavity and the amount of evaporation that evaporates in contact with the peripheral wall 31 are predicted. Control based on a comparison between the amount of adhesion and the amount of evaporation is performed.

FIG. 6 is a flowchart for determining the fuel injection start timing and the number of fuel injection stages. According to this flowchart, in step S1, the basic injection amount Q is calculated from the engine speed and load detected by a sensor or the like, taking into account the actual accelerator opening. Next, in step S2, a fuel adhesion amount Gd to the head cavity peripheral wall surface 31 is calculated. This Gd can be calculated by the following equation.
Gd = γ · X · Q

  γ is a coefficient for estimating how much fuel is in contact with the peripheral wall surface in the total injection amount, and γ = (period from when the spray tip contacts the peripheral wall surface until the end of spraying) / (total injection Period). X is a coefficient obtained from the injection pressure, the temperature Twall of the peripheral wall surface 31 and L / φd (see FIG. 3), and estimates the ratio of fuel adhering to the peripheral wall surface 31 as a liquid film. Is.

Next, in step S3, the evaporation amount Gv of the fuel in contact with the head cavity peripheral wall surface 31 is calculated. This Gv is a function having variables such as the temperature Twall of the peripheral wall 31, the ambient temperature Tamb in the combustion chamber 18, and the time τ from fuel attachment to top dead center. That is,
Gv = f (Gd, Twall, Tamb, τ)

  The temperature Twall of the peripheral wall surface 31 is detected by a wall temperature detection sensor (temperature detection means) 90. As the wall temperature detection sensor 90, a thermoelectric thermometer using a thermocouple or the like can be used. Further, the temperature detection means 90 is not limited to directly measuring the temperature of the peripheral wall surface 31, but, for example, measures the cooling water temperature in the cylinder or the cylinder head, and indirectly detects the temperature of the peripheral wall surface 31 from the cooling water temperature. May be estimated.

  In step S4, the adhesion amount Gd and the evaporation amount Gv are compared, and a difference ΔG (= Gd−Gv) is calculated. If ΔG is less than the predetermined threshold value Glimit in step S5, it is determined that there is little adhesion to the peripheral wall surface 31, and in step S6, the injection conditions are determined so as to perform fuel injection in the normal mode. .

  In step S5, when ΔG is equal to or greater than the threshold value Glimit, it is determined that there is much adhesion to the peripheral wall surface 31, and in step S7, the number of injection stages is divided into two and the injection amount ratio is determined. In step S8, the injection timing of the pre-stage injection (first stage injection) is calculated, and the above steps S2 to S5 are performed again for this injection. If further division is required in step S5, steps S7 and S8 are repeated. Through these steps, the injection conditions for the active mode are determined.

  When the number of injection stages is only switched to one or two stages (when the number of injection stages is not three or more), the process proceeds to step S7 ′ when ΔG is greater than or equal to the threshold value Glimit in step S5, and injection division calculation is performed. In step S8 ′, the pre-injection timing is calculated, and the injection condition is determined in step S6.

  FIG. 7 is a graph showing changes in the crank elapsed angle θ and the cylinder pressure P in correspondence with the fuel injection timing. FIG. 7A shows the case of the normal mode in which injection is performed only once near the top dead center of the compression stroke. In this case, since almost the entire injection amount of fuel is evaporated at once by the heat in the cylinder 10, a great amount of heat is taken away, and the pressure in the cylinder 10 is rapidly decreased by Δp before ignition. For this reason, a heat loss becomes large and it may misfire depending on conditions.

  On the other hand, FIG. 7B shows the case of the active mode in which two-stage injection is performed, that is, the injection before the top dead center of the compression stroke and the injection near the top dead center. In this case, since the amount of injection at each stage is reduced, the heat lost for the evaporation of the fuel is reduced, and the pressure drop (Δp ′) in the cylinder 10 is also suppressed. By injecting the second-stage fuel when the first-stage fuel self-ignites, the entire amount of fuel is self-ignited and the generation of white smoke is prevented.

  Therefore, as described above, when it is predicted that the amount of fuel adhering to the peripheral wall surface 31 of the head cavity 29 will increase, performing multiple stages of injection reduces the heat loss as seen in FIG. It is also possible to prevent misfire.

[Control method 2]
The fuel injection mode can also be selected as follows. FIG. 8 is a flowchart for determining the number of fuel injection stages and the fuel injection start timing. According to this flowchart, in step S1, the basic injection amount Q is calculated from the detected engine speed and load, and in step 2, it is determined whether or not the basic injection amount Q is equal to or greater than a predetermined value. As a result, when the basic injection amount Q is less than or equal to a predetermined value, it can be predicted that the amount of adhesion of the head cavity 29 to the peripheral wall surface 31 will not increase so much, so in step S6, the normal mode condition with one injection step is set. Determine.

  If the basic injection amount Q is equal to or greater than the predetermined value, the process proceeds to step S3, and it is determined whether or not the temperature Twall of the peripheral wall surface 31 is equal to or lower than a predetermined value, for example, the fuel evaporation temperature. If it is equal to or greater than the predetermined value, it can be predicted that the fuel that has contacted the peripheral wall surface 31 will evaporate. Therefore, in step S6, the condition for the normal mode in which the number of injection stages is one is determined.

  When the temperature Twall is equal to or lower than the predetermined value, the process proceeds to step S4, the number of fuel injection stages is calculated, the ratio of the injection amount is determined, the preceding injection timing is calculated in step S5, and the injection stage number is calculated in step S6. Determine the conditions of the active mode for multiple stages.

  According to this control method 2, it is possible to prevent the fuel from adhering to the peripheral wall surface 31 with simpler control than the control method 1.

[Other means for preventing fuel from adhering to the head cavity]
In the present embodiment, in order to prevent fuel adhesion to the peripheral wall surface 31 of the head cavity 29, the following two configurations are further provided.
(1) One of them is effective compression ratio changing means for changing the effective compression ratio of the combustion chamber in accordance with the (predicted) adhesion amount of fuel to the peripheral wall surface 31. As this effective compression ratio changing means, in this embodiment, re-opening of the exhaust valve 17B is adopted, and a variable valve operating device is used as the valve operating device 71 for opening and closing the exhaust valve 17B. The valve closing timing of the exhaust valve 17B by the device 71 is controlled by the valve gear ECU 84.

  In the re-opening of the exhaust valve 17B, the exhaust valve 17B is temporarily opened in the initial stage of the compression stroke to obtain an effective compression ratio lower than the apparent compression ratio. The effective compression ratio is freely changed by changing the closing time.

  The exhaust variable valve operating device 71 is conventionally known, such as a configuration in which the valve closing timing is variable depending on the shape of the valve operating cam, a configuration in which the valve is opened and closed using an electric actuator, and the valve closing timing is variable. Any configuration of can be adopted.

  The exhaust variable valve device 71 is controlled as follows. That is, when ΔG calculated in step S4 in the flowchart of FIG. 6 is equal to or greater than a predetermined value (when the adhesion amount Gd is large), the valve closing timing for reopening is advanced and the effective compression ratio is increased. Thereby, since the temperature in the cylinder 10 is raised to a high temperature at an early stage, the evaporation of the fuel is promoted and the adhesion of the fuel to the peripheral wall surface 31 is suppressed.

  On the other hand, when ΔG is less than a predetermined value (when the adhesion amount Gd is small), the valve closing timing for re-opening is delayed to lower the effective compression ratio.

  In addition, in order to obtain an appropriate effective compression ratio, the exhaust valve 17B is reopened in the above, but other means may be used. For example, the intake valve operating device 70 may be configured to be variable, and the optimum effective compression ratio may be acquired by early closing or late closing of the intake valve 17A at the end of the intake stroke.

  (2) The second is a heater (heating device) that controls the temperature of the peripheral wall surface 31 of the head cavity 29. As shown in FIG. 3, the head cavity 29 is provided with a heater (heating device) 93 that heats the peripheral wall surface 31. Specifically, a heater 93 such as a glow heater is provided so as to be in contact with the back side of the fuel collision portion 34, and a heat insulating layer 94 is formed between the heater 93 and the cylinder head 12.

  By providing such a heater 93, it is possible to help evaporate the fuel in contact with the peripheral wall surface 31 of the head cavity 29, and it is possible to more reliably prevent the generation of white smoke accompanying the adhesion of fuel.

  The heater 93 is connected to the output portion of the engine controller 66 and is controlled based on the temperature of the peripheral wall surface 31 detected by the wall temperature detection sensor 90. That is, when the temperature of the peripheral wall surface 31 (collision part 34) is lower than a predetermined target value, the heater temperature is controlled to increase. Therefore, when the temperature of the peripheral wall surface 31 is low, such as when the engine is started, the heater temperature is raised to promote evaporation, and when the engine is warmed, the heater temperature is lowered to suppress energy consumption. it can.

  Although the heater 93 can be provided on the entire circumference of the head cavity peripheral wall surface 31, it can be partially provided only on the portion where the fuel collides. For example, as shown in FIG. 9, when the fuel injection nozzle has eight fuel injection ports 44 radially, eight heaters are provided on the peripheral wall surface 31 corresponding to each fuel injection port 44. be able to.

  As a result, the space in which the fuel is present can be intensively heated, and efficient evaporation characteristics can be obtained. Moreover, energy consumption can be reduced.

  The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate.

  The present invention can be applied to a compression self-ignition internal combustion engine such as a diesel engine, and is suitable for an internal combustion engine that performs fuel injection mainly near the top dead center of the compression stroke (range of top dead center ± 40 °).

1 is a schematic view of a diesel engine that is a compression premixed internal combustion engine according to an embodiment of the present invention. It is sectional drawing of the cylinder top part of the diesel engine to which this invention is applied. It is sectional drawing which expands and shows a head cavity and a fuel injection nozzle. FIG. 4 is a cross-sectional view taken along arrow IV-IV in FIG. 2. It is a time chart which shows the injection pattern of the fuel by a fuel injection nozzle. 4 is a flowchart for determining the number of fuel injection stages and the fuel injection start timing. It is a graph which shows the change of crank passage angle and cylinder pressure. 4 is a flowchart for determining the number of fuel injection stages and the fuel injection start timing. It is a top view of the head cavity seen from the piston side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piston 12 Cylinder head 13 Fuel injection nozzle 28 Explosion surface 29 Head cavity 31 Perimeter wall surface 66 Engine controller 71 Exhaust variable valve gear 90 Temperature detection means 93 Heater

Claims (7)

Compression self-ignition in which a concave head cavity is provided on the explosion surface of the cylinder head facing the top surface of the piston, and a fuel injection nozzle for injecting fuel toward the peripheral wall surface of the head cavity is provided in the head cavity In the internal combustion engine,
Temperature detecting means for detecting the temperature of the peripheral wall surface of the head cavity;
A controller for setting the fuel injection timing and the number of injection stages based on the detected peripheral wall temperature ,
The controller predicts the amount of fuel adhering to the peripheral wall surface of the head cavity and the amount of fuel evaporated in contact with the peripheral wall surface based on the temperature of the peripheral wall surface detected by the temperature detecting means. A compression ignition type internal combustion engine having a function of setting the fuel injection timing and the number of injection stages based on a comparison with the quantity .   The controller has a function of setting the first stage injection amount in a range of 30% to 50% of the total injection amount when the number of injection stages is divided into two stages. A compression self-ignition internal combustion engine as described in 1.   When the controller divides the number of injection stages into two stages, the first stage injection start timing is set before the compression stroke top dead center so that the self-ignition accompanying the first stage injection is performed near the compression stroke top dead center. 2. The compression ignition type internal combustion engine according to claim 1, wherein the internal combustion engine has a function of setting within a range of 40 [deg.] To 0 [deg.]. An effective compression ratio changing means for changing the effective compression ratio in the cylinder is provided, and the effective compression ratio is increased when the adhesion amount is equal to or greater than the evaporation amount, and the effective compression ratio is decreased when the adhesion amount is less than the predetermined value. as such, the effective compression ratio changing means, characterized in that is controlled compression ignition type internal combustion engine according to claim 1.   The compression self-ignition internal combustion engine according to claim 1, further comprising a heater for heating a peripheral wall surface of the head cavity. 6. The compression autoignition according to claim 5 , wherein the heater is controlled so that the temperature rises when the detected peripheral wall surface temperature is lower than a predetermined target value and decreases when the detected temperature is higher. Internal combustion engine. 6. The compression self-ignition internal combustion engine according to claim 5 , wherein the heater is provided partially corresponding to a portion where fuel on the peripheral wall surface of the head cavity collides.

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